A third Generation Partnership Project (3GPP) mobile communication system based on a Wideband Code Division Multiple Access (WCDMA) radio access technology has widely deployed all over the world. High Speed Downlink Packet Access (HSDPA), which can be defined as the first evolution stage of the WCDMA, provides the 3GPP mobile communication system with high competitiveness in the mid-term future. However, since the requirements and expectations of users and service providers continuously increase and the development of a competing radio access technology is in progress, there is a need for a new technology evolution in the 3GPP for further competitiveness.
One of systems that are considered in the post third-generation systems is an Orthogonal Frequency Division Multiplexing (OFDM) system which can attenuate an Inter-Symbol Interference (ISI) with low complexity. In the OFDM system, pieces of data that are input in series are transformed into N pieces of parallel data and then transmitted through N subcarriers. The subcarriers have orthogonality with each other. Orthogonal Frequency Division Multiple Access (OFDMA) refers to a multiple access scheme of realizing multiple access by independently providing each user with part of subcarriers.
One of the major problems of the OFDM/OFDMA system lies in that Peak-to-Average Power Ratio (PAPR) can be very high. The PAPR problem is that the peak amplitude of a transmit signal is very higher than a mean amplitude. It has its origin in that an OFDM symbol is constructed by overlapping N sinusoidal signals on different subcarriers. The PAPR is related to the capacity of the battery and problematic in user equipment sensitive to power consumption. To reduce power consumption, it is necessary to lower the PAPR.
One of systems that have been proposed to lower the PAPR is Single Carrier-Frequency Division Multiple Access (SC-FDMA). The SC-FDMA is of a type in which Frequency Division Multiple Access (FDMA) is combined with a Single Carrier-Frequency Division Equalization (SC-FDE). The SC-FDMA has a similar characteristic to that of OFDMA in that data is modulated and demodulated in time domain and frequency domain by employing Discrete Fourier Transform (DFT), but is advantageous in transmission power saving because the PAPR of a transmit signal can be lowered. In particular, it can be said that SC-FDMA is advantageous in uplink direction in which communication is performed from a user equipment to a base station, which is sensitive to transmission power in relation to the battery capacity of the user equipment.
Important things when the user equipment transmits data to the base station are small bandwidth and wide coverage. The SC-FDMA system has wider coverage than that of other system when using the same power amplifier is provided.
Data includes user data and a control signal concerned with the user data. A transmitter can transmit only the control signal and can also transmit the user data and the control signal by multiplexing them. If transmission of the control signal is failed, a receiver does not know even whether user data has been sent. Accordingly, transmission of the control signal requires high reliability.
Since radio resources used for transmitting the control signal may limit data rate, it is better that radio resources necessary for transmitting the control signal are small. Also, a number of terminals exist within one cell. It is therefore necessary for a base station to identify a user equipment which has sent the control signal.
There is a need for a method of allowing a user equipment to transmit a control signal to a base station with high reliability.